Spinal cord stimulation (SCS) is an advanced treatment option for chronic pain. It is most used to treat chronic low back and leg pain. SCS has been around since the 1960s and has evolved greatly over the years. In this article, we provide a brief history of SCS and review some of the most significant updates to SCS technology that are in use today.
What does spinal cord stimulation involve?
Before we get into the history, here’s a quick rundown of what SCS involves:
- Two leads containing electrodes are inserted into the epidural space surrounding the spinal cord. The leads are positioned so that they stimulate the spinal nerves that are sending pain signals from the limbs or torso to the brain.
- An implantable pulse generator (IPG) is placed under the skin, usually above the buttocks. Extension wires connect the IPG to the leads in the spine.
- The IPG is programmed to send pulses of electricity to the leads. This stimulates specific nerve cells near the leads and blocks pain signalling.
- The shape of the pulses is called the stimulation waveform. Reprogramming can change the way the stimulation feels and how it affects the spinal cord.
- Traditional stimulation produces a tingling, pins-and-needles feeling called paraesthesia.
History of spinal cord stimulation
A timeline of major developments in SCS technology is pictured below. We’ll go over each one in a little more detail.
Early spinal cord stimulation devices
The first SCS device was tested in humans in 1967 and the first commercially available system was released in 1968.
The first stimulator was very bulky. It consisted of an implanted receiver connected to a simple electrode in the spinal canal. It was powered externally through a round antenna placed on the skin over the implant, which was connected to a battery-operated transmitter device.
The first fully implantable system became available in 1981. The design was based on cardiac pacemakers.
Stimulator lead updates
The first SCS leads had a “paddle” design. Implanting paddle leads requires an open surgery, called a laminectomy. This involves cutting into the vertebra (back bones) of the spine. Paddle leads designs have advanced greatly over the years and are still used today.
Percutaneous leads
In 1975, the percutaneous (“inserted through the skin”) lead was developed. These thin leads are inserted into the epidural space with a spinal needle. This makes implant surgery much easier and less invasive. They were initially used for trialling SCS therapy but were soon adopted for permanent use. They are a popular choice today.
Multi-contact electrodes
The 1980s saw major updates to electrodes with the development of multi-contact electrodes. The first electrodes had a single contact. This meant they had to be placed precisely on the patient’s “sweet spot” for pain relief. With multiple contacts, different electrode combinations can be programmed, and the configuration of stimulation can be adjusted to optimise each patient’s pain relief. This is especially helpful if the leads move a little and minimises the need for further surgery.
System updates
Rechargeable systems
In 2004, the first rechargeable IPG became available. Before this, IPGs had to be replaced roughly every 4 years. Rechargeable systems are much smaller and longer lasting.
MRI-compatible devices
In 2013, the first MRI-compatible became available. This allowed patients to have full body MRI scans (under certain conditions). This is important for chronic pain patients with spinal issues who need imaging.
Wireless spinal cord stimulation
In 2014, the world’s first wireless SCS system became available. The stimulator consists of a thin lead with a tiny receiver. There is no IPG. Instead, it is wirelessly powered by a small external transmitter worn on the body. The stimulator implant is so small that it is injected into position with a needle.
Stimulation updates
New waveforms
By modifying the stimulation parameters, new waveforms have been developed that may have different effects on the spinal cord. The parameters include:
- Amplitude (or voltage) – the strength of the pulse
- Pulse width – how long each pulse is (in micro-seconds)
- Frequency – the number of pulses per second (in Hertz)
The stimulation can be delivered at a constant, steady rate (called “tonic” stimulation) or in bursts.
- Traditional stimulation is tonic, low frequency, and has a higher amplitude. This produces paraesthesia (tingling sensation).
In 2015 and 2016, two new SCS waveforms were approved: burst SCS and high-frequency SCS. These waveforms are paraesthesia-free – you don’t feel the stimulation. Studies have found them to be useful “rescue” options for patients who don’t get enough pain relief with traditional stimulation or find that it no longer works for them.
- Burst SCS delivers high frequency stimulation (50Hz) in short on/off bursts – about 40 bursts per second.
- High-frequency SCS delivers small electrical pulses at a very high frequency – up to 10,000 Hz (traditional stimulation is around 50Hz). Studies have shown high-frequency SCS can be more effective than traditional SCS for patients with mainly back pain.
- High-density (or high-dose) SCS offers another rescue option for SCS patients. It delivers very long pulses with a smaller amplitude and a higher frequency. Paraesthesia is reduced or not noticeable.
New stimulation targets
In 2020, differential target multiplexed SCS became available. This uses multiple electrical signals (frequencies) to target different areas of the spinal cord and stimulate a different type of cell: glial cells (in addition to nerve cells). Glial cells help to support nerve cells and play an important role in chronic pain.
Adaptive stimulation
In 2022, closed-loop SCS was approved. Closed-loop SCS systems constantly monitor the response of the spinal cord to the stimulation. The stimulation is automatically adjusted to optimise pain relief and reduce any uncomfortable stimulation (for example, when changing body position).
In summary...
- SCS is an advanced therapy with a long history of use, but that doesn’t mean it’s an outdated treatment option.
- SCS has come a long way since the 1960s and continues to evolve and improve.
- There have been many improvements to the device hardware (IPG and leads).
- More recent developments have focused on stimulation programming (waveforms).
- We now have access to a range of SCS devices and new waveforms.
- Eligible patients should discuss their best options with their pain physician.
References & Resources:
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2. Lam CM, et al. “Advances in Spinal Cord Stimulation”. 2023; 10(2): 185. https://www.mdpi.com/2306-5354/10/2/185
3. London D and Mogilner A. “Spinal Cord Stimulation: New Waveforms and Technology”. N2022; 33(3): 287-295. https://doi.org/10.1016/j.nec.2022.02.006
4. North RB, et al. “Spinal cord stimulation for chronic, intractable pain: superiority of “multi-channel” devices”. 1991; 44(2): 119-130. https://doi.org/10.1016/0304-3959(91)90125-H
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9. “Medtronic introduces first MRI-safe neurostimulation system for chronic pain”. 2013, 6 August. https://neuronewsinternational.com/medtronic-introduces-first-mri-safe-neurostimulation-system-for-chronic-pain/
10. “Stimwave Freedom-8A spinal cord stimulation system receives FDA clearance”. 2015, 17 December. https://neuronewsinternational.com/stimwave-freedom-8a-spinal-cord-stimulation-system-receives-fda-clearance/